Let me try to give some insides. First of all gvm-feed-update.
gvm-feed-update is NOT maintained by Greenbone and is therefore not used anywhere in our docs or provided code by Greenbone. It’s maintained by the Kali/Debian packagers and as far as I know it just calls the standard greenbone-*-sync scripts provided by us in one go. Personally I think you should not use it.
greenbone-certdata-sync is just the same as greenbone-feed-sync --type CERT. It is/was just provided for backwards compatibility. It doesn’t get installed anymore (by default) since gvmd 22.5.0.
greenbone-scapdata-sync is just the same as greenbone-feed-sync --type SCAP. It is/was just provided for backwards compatibility. It doesn’t get installed anymore (by default) since gvmd 22.5.0.
greenbone-nvt-sync is the old sync script written in bash to download the vulnerability tests data (nasl and notus files). It is deprecated since openvas-scanner 22.6.0.
/usr/sbin/greenbone-feed-sync is the old sync script written in bash to download the CERT, SCAP and GVMD data. It doesn’t get installed anymore (by default) since gvmd 22.5.0.
There is a new greenbone-feed-sync script written in Python to replace all of the above scripts. See the announcement at New greenbone-feed-sync script This script hasn’t been picked up by the distributions yet but hopefully will arrive in the next months.
Even the gvm-feed-update use case is supported because by default when not passing any arguments --type all is run which downloads all types of feed data.